1. Field of the Invention
The present invention relates to a Global Positioning System (GPS). More particularly, the invention relates to a global positioning system including at least one GPS satellite that transmits a GPS radio wave, at least one GPS base station, and at least one GPS terminal that generates positional information on the terminal itself on the surface of the earth, in which the reception state or condition of the terminal is optimized so as to compensate degradation of the GPS radio wave the terminal received due to cosmic and/or atmospheric noise with the use of a control signal from the at least one base station.
2. Description of the Related Art
Generally, the intensity or strength of the GPS radio wave transmitted from a GPS satellite at the earth""s surface is approximately constant. Specifically, the intensity is typically kept at approximately xe2x88x92130 dBm. Therefore, the radio section of a GPS terminal is designed to conduct its operation optimally at the typical intensity of approximately xe2x88x92130 dBm.
However, actually, the radio wave intensity at the earth""s surface tends to fluctuate due to extrinsic noise, such as cosmic noise and atmospheric noise. Also, it is affected by interference wave with another radio system.
Thus, if the radio section of the GPS terminal receives the GPS radio wave affected by the extrinsic noise, there arises a problem that the GPS terminal is unable to recognize its position accurately on the earth""s surface. As a result, there has been the need to solve this problem.
Accordingly, an object of the present invention is to provide a global positioning system that ensures accurate recognition of the position of a GPS terminal even if the radio section of a GPS terminal receives the GPS radio wave affected by extrinsic noise.
Another object of the present invention is to provide a global positioning system that makes it possible to optimize reception operation of a GPS radio wave even if the radio section of a GPS terminal receives the GPS radio wave affected by extrinsic noise.
Still another object of the present invention is to provide a global positioning system that eliminates the effect by an interference radio wave with another radio system.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A global positioning system according to a first aspect of the present invention comprises:
(a) at least one GPS terminal for receiving a GPS radio wave transmitted from a GPS satellite and for generating positional information of the terminal based on information contained in the radio wave received; and
(b) a GPS base station for detecting degradation of the GPS radio wave due to extrinsic noise and for transmitting a control signal containing information on the degradation of the radio wave to the at least one terminal;
wherein the at least one terminal conducts its operation to optimize reception condition or state of the GPS radio wave based on the control signal received.
With the global positioning system according to the present invention, when the strength or intensity of the GPS radio wave on the surface of the earth (i.e., arriving radio wave intensity at the earth""s surface) degrades due to extrinsic noise such as cosmic noise (e.g., solar noise) and/or atmospheric noise (e.g., rainfall-inducing noise) and/or interference radio waves, the GPS base station detects the degradation of the GPS radio wave. Then, the base station transmits the control signal containing the information on the degradation of the GPS radio wave to the at least one GPS terminal by way of an appropriate radio medium (e.g., a mobile telephone network). On the basis of the information in the control signal transmitted by the base station, the terminal conducts its operation to optimize reception condition or state of the GPS radio wave.
As a consequence, even if the strength or intensity of the GPS radio wave on the earth""s surface (i.e., the arriving radio wave intensity at the earth""s surface) degrades due to some extrinsic noise or interference radio waves, the GPS terminal can receive the radio wave transmitted at the optimum condition or state.
In a preferred embodiment of the system according to the invention, the at least one terminal comprises a function to eliminate the degradation of the GPS radio wave due to an interference radio wave.
In another preferred embodiment of the system according to the invention, the at least one terminal comprises a receiver for receiving the control signal transmitted from the base station, an amplifier for amplifying a signal contained in the GPS radio wave, and a gain controller for controlling a gain of the amplifier. The gain controller adjusts the gain of the amplifier according to the information contained in the control signal about the degradation of the GPS radio wave.
In this embodiment, it is preferred that the gain controller increases the gain of the amplifier by increasing a current supplied to the amplifier.
In still another preferred embodiment of the system according to the invention, the at least one terminal comprises a receiver for receiving the control signal transmitted from the base station, an amplifier for amplifying a signal contained in the GPS radio wave, and a gain controller for controlling a gain of the amplifier. The gain controller adjusts the gain of the amplifier according to the information contained in the control signal about the degradation of the GPS radio wave. The gain controller increases the gain of the amplifier to lower an impedance of the amplifier and restricts a bandwidth of a peripheral circuit of the amplifier, thereby suppressing a noise component of an output of the amplifier.
In this embodiment, it is preferred that an additional amplifier is further provided after the amplifier. A gain of the additional amplifier is controlled in such a way as to prevent a total gain of the amplifiers from being excessive.
In this embodiment, it is preferred that a band-pass filter is further provided after the amplifier. A passband of the band-pass filter is controlled in such a way as to suppress the noise component of the output of the amplifier.
In this embodiment, a band-pass filter may be further provided between a GPS antenna and the amplifier. A passband of the band-pass filter is controlled in such a way as to suppress the noise component of the output of the amplifier.
In a further preferred embodiment of the system according to the invention, a noise eliminator is additionally provided for eliminating a noise component of the amplifier.
In this embodiment, preferably, the noise eliminator identifies a noise frequency band of an interference radio wave by detecting a peak frequency of the interference radio wave. The noise eliminator eliminates the noise frequency band.
In this embodiment, preferably, the noise eliminator includes a function of eliminating a noise component of the amplifier higher than a specific level.
A GPS terminal according to a second aspect of the invention comprises:
(a) an antenna for receiving a GPS radio wave transmitted from a GPS satellite, producing an output;
(b) a radio section for amplifying the output of the antenna, producing an output;
(c) a decoder for decoding the output of the radio section, generating positional information of the terminal based on information contained in the radio wave received; and
(d) a gain controller for controlling a gain of the radio section;
wherein the radio section receives a control signal about degradation of the GPS radio wave due to extrinsic noise transmitted from a base station;
and wherein the gain controller controls the radio section in such a way that reception operation of the terminal for the GPS radio wave is optimized based on the control signal received.